x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 114 insertions, 0 deletions

diff --git a/Documentation/process/index.rst b/Documentation/process/index.rst
new file mode 100644
index 000000000..aa7c959a5
--- /dev/null
+++ b/Documentation/process/index.rst
@@ -0,0 +1,114 @@
+.. raw:: latex
+
+	\renewcommand\thesection*
+	\renewcommand\thesubsection*
+
+.. _process_index:
+
+=============================================
+Working with the kernel development community
+=============================================
+
+So you want to be a Linux kernel developer?  Welcome!  While there is a lot
+to be learned about the kernel in a technical sense, it is also important
+to learn about how our community works.  Reading these documents will make
+it much easier for you to get your changes merged with a minimum of
+trouble.
+
+An introduction to how kernel development works
+-----------------------------------------------
+
+Read these documents first: an understanding of the material here will ease
+your entry into the kernel community.
+
+.. toctree::
+   :maxdepth: 1
+
+   howto
+   development-process
+   submitting-patches
+   submit-checklist
+
+Tools and technical guides for kernel developers
+------------------------------------------------
+
+This is a collection of material that kernel developers should be familiar
+with.
+
+.. toctree::
+   :maxdepth: 1
+
+   changes
+   programming-language
+   coding-style
+   maintainer-pgp-guide
+   email-clients
+   applying-patches
+   backporting
+   adding-syscalls
+   volatile-considered-harmful
+   botching-up-ioctls
+
+Policy guides and developer statements
+--------------------------------------
+
+These are the rules that we try to live by in the kernel community (and
+beyond).
+
+.. toctree::
+   :maxdepth: 1
+
+   license-rules
+   code-of-conduct
+   code-of-conduct-interpretation
+   contribution-maturity-model
+   kernel-enforcement-statement
+   kernel-driver-statement
+   stable-api-nonsense
+   stable-kernel-rules
+   management-style
+   researcher-guidelines
+   generated-content
+   coding-assistants
+   conclave
+
+Dealing with bugs
+-----------------
+
+Bugs are a fact of life; it is important that we handle them properly. The
+documents below provide general advice about debugging and describe our
+policies around the handling of a couple of special classes of bugs:
+regressions and security problems.
+
+.. toctree::
+   :maxdepth: 1
+
+   debugging/index
+   handling-regressions
+   security-bugs
+   threat-model
+   cve
+   embargoed-hardware-issues
+
+Maintainer information
+----------------------
+
+How to find the people who will accept your patches.
+
+.. toctree::
+   :maxdepth: 1
+
+   maintainer-handbooks
+   maintainers
+
+Other material
+--------------
+
+Here are some other guides to the community that are of interest to most
+developers:
+
+.. toctree::
+   :maxdepth: 1
+
+   kernel-docs
+   deprecated